It is earlier known to use devices having e.g. gas bearings for axial and radial supporting of rotatable elements. Such a device is shown e.g. in European patent application No. 82201555.8 bearing the publication No. 0082548. This bearing gives low friction and thereby possibilities of using high rotational speeds without big power losses. Using higher speeds in the known device necessitates that the rotatable element is accurately balanced and centered in the bearing device. Vibrations caused by imbalance can easily damage a bearing taking up radial forces and also the machine members connected to the bearing.
In the device accordingly to the above-mentioned publication, the rotatable elements is subjected to axial load by aid of magnetic means until contact is obtained in the thrust bearing, which implies that the element can be removed by being pulled axially from a central shaft journal, which guides the element in radial direction and has a radial bearing surface. Exchange of the element thus requires a considerable free space axially outside the device and requires an accurate aligning of the element on the shaft journal at assembly. The shaft journal and the tubular shaft of the rotatable element arranged thereupon gives the device a big axial extension.
Thrust bearings in which a rotatable element is arranged to cooperate with a plain surface upon a supporting member and is freely displaceable in radial direction upon this surface are earlier known. A slot between the rotatable element and the supporting element can thereby be maintained by introduction of a pressure medium between the elements, e.g. according to European patent application No. 0061016. This publication, however, does not show how the movable element shall be held in desired position upon the plain surface of the supporting element.
The slot can be maintained by electromagnetic means, e.g. according to U.S. Pat. No. 4,147,396. Magnetic attraction forces hereby give a centering effect on the rotatable element. A complicated control of the electric current to the magnets is, however, required in order to maintain a desired slot height, which makes the device expensive and has a negative influence upon the reliability of service.